A typical pneumatic tire includes a body ply and belts as members forming the tire framework. A body ply includes a number of parallel cords and rubber coating the cords. The cords of a body ply extend along the radial direction of the tire at the sides of the tire. A belt also includes a number of parallel cords and rubber coating the cords. The cords of a belt are inclined relative to the circumferential direction of the tire. Tires having such body plies and belts are typically mass-manufactured.
Body plies and belts are manufactured in the following manner. A great number of, that is, five hundred to two thousand cords that are made of organic fibers or metal filaments are arranged in parallel and are run along the longitudinal direction. The group of the parallel cords is coated with rubber from both sides by a calender to form a body ply cloth and a belt cloth. Typically, the cloths are wound and stored. As necessary, the cloths are sent to the subsequent manufacturing steps.
In the subsequent steps, the body ply cloth is unwound. The body ply cloth is then successively cut along a direction perpendicular to the longitudinal direction (longitudinal direction of the cords). As a result, a number of narrow sheets are obtained. The measurement of each sheet along the longitudinal direction of the cords substantially corresponds to the width of one tire. The direction perpendicular to the longitudinal direction of the cords corresponds to the longitudinal direction of the sheets. The sheets are joined at the ends in the longitudinal direction to form a long sheet. The long sheet is wound and stored. In a body ply using organic cords, the sheets are partly overlapped as shown by chain double-dashed lines in FIG. 27 when being joined. In FIG. 27, numeral 102 indicates an overlapped joint.
In the subsequent steps, the belt cloth is unwound. The unwound belt cloth is cut along a direction inclined relative to the longitudinal direction (longitudinal direction of the cords) to form a number of narrow sheets. Each sheet has a width corresponding to one or two tires. As in the case of the narrow sheets for body ply, the narrow sheets for belt are joined at the ends in the longitudinal direction to form a long sheet. The long sheet is wound and stored. The sheets are butted against each other as shown by chain double-dashed lines in FIG. 31 when being joined. In FIG. 31, numeral 108 indicates a butted joint.
The wound body ply long sheet and the wound belt long sheet are unwound in subsequent steps and cut to obtain sheet pieces each having a length and a width corresponding to a single tire. Then, the sheets are joined at the ends to be annular on a forming drum. A body ply and belts are thus formed. The sheet pieces of the body ply, in which organic fibers are used, are joined by overlapping the ends as shown by solid line in FIG. 27. The sheet pieces of the belt, in which steel cords are used, are joined by butting the ends as shown by solid lines in FIG. 31. In FIG. 27, numeral 103 indicates an overlapped joint when the body ply sheet pieces are formed into an annular body. In FIG. 31, numeral 200 indicates a butted joint when the belt sheet pieces are formed into an annular body. Therefore, a finished annular body ply 101 has the overlapped joints 103 in addition to the overlapped joints 102. A finished annular belt has the butted joints 200 in addition to the butted joints 108.
A pneumatic tire having the above body ply and belts have the following drawbacks.
First, drawbacks of the body ply 101 will be described. As shown in FIGS. 28 to 30, the cord interval R1 (see FIG. 27) in the overlapped joints 102, 103 is narrower than the cord interval R2 in the parts other than the overlapped joints 102, 103 (see FIG. 27). FIG. 28 diagrammatically shows the cord intervals R1, R2 of the body ply 101. Specifically, FIG. 28 shows the cord intervals R1, R2 in the vicinity of the humps when viewed in the axial direction of the tire (when viewed from a side). A circle 104 of FIG. 28 indicates a case where the cord intervals of the body ply 101 are 1 mm at any point in the circumference of the tire. An undulating annular line 105 represents the actual cord intervals of the body ply 101. FIG. 29 shows the cord intervals in the vicinity of an overlapped joint 102 when the narrow sheets are joined. FIG. 30 shows the cord intervals in the vicinity of an overlapped joint 103 when the body ply is formed into an annular body. As obvious from FIGS. 28 to 30, the cord intervals are smaller (the cords are denser) at the overlapped joints 102, 103 than in the other portions.
In the calender process, the cord intervals are inevitably made different between groups of the parallel cords at the center and groups of the parallel cords at the sides. Cloth formed with the calender therefore has uneven cord intervals in the lateral direction.
The width of a cloth manufactured by the calender, or the length of the narrow sheets obtained by cutting the cloth, is generally shorter than the circumference of a tire although there are exceptions depending on the sizes of the tires. Therefore, as obvious from FIG. 28, the sheet pieces needed for forming a body ply 101 in one tire has at least one overlapped joint 102. Thus, the finished body ply 101 has the overlapped joints 102 between the narrow sheets and the overlapped joints 103 between the ends of the sheet pieces. The locations and the numbers of the overlapped joints differ from one tire to another. In addition, when winding and unwinding sheet material for body plies, tension is applied to the sheet material, which increases the unevenness of the cord intervals.
As a result, as obvious in FIGS. 27 to 30, a finished body ply has randomly arranged overlapped joints 102, 103, which greatly vary the cord intervals. The cord intervals are uneven over the entire circumference of the tire.
Next, drawbacks of the belt will now be described. To prevent the steel cords 109 from being stacked, the cord 109 is removed at the butted joint 108 between the narrow sheets and at the butted joint 200 between the sheet pieces as shown in FIG. 31. The removed cord 109 is shown by chain double-dashed line.
Therefore, as shown in FIGS. 32 to 34, the cord interval S1 (see FIG. 31) in the butted joints 108, 200 is wider than the cord intervals S2 in the parts other than the butted joints 108, 200 (see FIG. 31). As in the case of the body ply, the length of the narrow sheet is generally shorter than the circumference of the tire. Therefore, a finished belt has at least two butted joints 108, 200. In addition, as in the case of the body ply, the locations and the numbers of the butted joints differ from one tire to another. Also, tension applied to the belt during manufacture increases the unevenness of the cord intervals.
A tire having the above body ply and the belts is not satisfactory in terms of the consistency as a product.
The unevenness of the cord intervals in the body ply and the belts described above creates an uneven weight distribution in the circumferential direction of the tire. The degree of the unevenness of the weight distribution differs from one tire to another.
To reduce the imbalance, the weight balance is measured when the tire is attached to a wheel, and led weights are attached to sections of the wheel rim as necessary. However, the balance measurement and the attaching of the weights are troublesome and increase the cost. While the vehicle is running, an impact applied to the wheel can remove the weights from the wheel rim. In this case, the weight balance of the tire in the circumferential direction is disturbed, which causes the vehicle body to vibrate.
Japanese Laid-Open Patent Publication No. 49-76978, corresponding to U.S. Pat. No. 3,826,297, discloses a technology for forming plies and belts. In this technology, ribbons that are coated with rubber and reinforced with cords are arranged such that the sides are butted against each other. Japanese Laid-Open Patent Publication No. 2001-145961, corresponding to European Patent No. EP1226926, discloses a technology for forming annual plies. In this technology, a cylindrical body is formed by consecutively winding a ribbon that is coated with rubber and reinforced with cords. The cylindrical body is cut to form plate bodies. The annular ply is formed with the plate bodies.
An objective of Japanese Laid-Open Patent Publication 49-76978 (U.S. Pat. No. 3,826,297) is to form radial tire frameworks with a simple apparatus. An objective of Japanese Laid-Open Patent Publication No. 2001-145961 (EP 1226926) is to form plies at low cost without using a large apparatus. However, these publications do not present any concept of making the cord intervals in rubber coated ribbons uniform or of making the cord intervals in the circumferential direction of a tire to manufacture tires having an improved weight balance.